For this, it's easiest to have 7-zip installed (this article will only cover this method).  The download page can be found here: https://www.7-zip.org/download.html

Once installed, locate the Excel file with protection and right-click it, go to 7-Zip -> Open archive

Navigate to the "xl" directory and edit "workbook.xml" in a text editor.

Find the workbookProtection tag as seen below, and delete the entire highlighted area (actual text may vary; just make sure to delete the entire tag):

Save and close the editor then click "OK" in the 7-Zip prompt to update the file within the archive; close the archive.

The Excel file can now be opened and have modifications made without a password.